Study On Fabrication And Properties Of PcBN With High Entropy Ceramics Binder

Commercial PcBN tool materials are generally divided into two grades:high content cBN and low content cBN.The former PcBN binder is composed of ceramic phase,which contains 80%～95%cBN,while the latter usually consists of ceramic bonder such as Ti（C,N）and Al N,which contains 50%to 80%cBN.In general,PcBN with higher cBN content will have higher hardness and thermal conductivity,which makes high cBN content PcBN more suitable for machining high hardness alloys and tissues materials containing hard points,such as chilled cast iron,cemented carbide,heat-resistant alloys and other materials that are widely used in automotive,aerospace and heavy industry.Suitable PcBN tools will have higher efficiency and better machining accuracy,so the research of PcBN bonder with high cBN content is very important.In this paper,TiN_0.3/TiB_1.8/Al/ZrO₂（abbreviated A4）,Transition metal carbide/TiN_0.3/TiB_1.8/Al/Zr O₂（HECC-A4）,andTransitionmetal boride/TiN_0.3/TiB_1.8/Al/Zr O₂（HECC-A4）instead of conventional metal or ceramic bond as high cBN content PcBN bonding agent.Mechanical alloying and high-temperature and high-pressure sintering were used to prepare PcBN.The effects of binder type,sintering temperature,cBN particle size and binder content on the organization and properties of PcBN sintered bodies were investigated by XRD,Raman,SEM and EDS,thermal analysis analytical methods and property tests such as hardness,fracture toughness and wear ratio.The results show that with the increase of cBN content,the particle size of cBN decreases.When the content is 90 vol.%and 95 vol.%,the binder is directly bonded to the surface of cBN,which makes some cBN particles directly contact with each other.The PcBN of the three binders is greatly affected by the content of cBN.When the content of cBN is 90 vol.%,the hardness and fracture toughness of PcBN reach the best.Three kinds of binder of HECC-A4 combined with PcBN best performance,as follows:3225 HV and9.10 MPa?m^1/2;Followed by HECB-A4 combined with PcBN:3254 HV and 8.98 MPa?m^1/2;Finally for A4 combined with PcBN:2908 HV and 7.71 MPa?m^1/2.With the increase of temperature,the structure of PcBN with 85 vol.%cBN becomes denser and the overall performance improves,because some reactions fail to occur at lower temperature.HECC-A4 bonded PcBN internally produced high entropy ceramic phases（Ti,V,Zr,Nb,Hf,Ta,Mo,W）C,and secondary phases such as Hf Ta C₂ and Hf Ta₂VC₄.HECB-A4 bonded PcBN produced high entropy ceramic（Al,Ti,V,Cr,Nb,Mo,Ta）B₂ with P6/mmm（191）structure in addition to medium entropy ceramic（Zr,Nb,Hf,Ta）N with Fm-3m（225）structure.Thermal analysis of the PcBN with the best mechanical properties showed that its initial oxidation and softening temperatures meet the requirements for dry cutting of tools.